Rock drilling bit

ABSTRACT

The present rock drilling bit comprises along its shaft portions of asymmetrical cross sectional areas for strengthening the drilling bit. These asymmetrical portions are distributed along and around the central axis of the shaft in such a manner that a curve which interconnects the surface centers of gravity of these portions which are located off said central axis, forms a spiral helix. These portions may be located in preferred sections of the drill bit shaft, especially in a transitionary section between the tip of the drill bit and the shaft proper or in another transitionary section between the shaft and a shank of the drilling bit.

United States Patent Boehm et al.

[54] ROCK DRILLING BIT [72] Inventors: Otto Boehm, Starnberg; Werner Scholz, Soecking, both of Germany Assignee: Werkzeugbau GmbH,

Germany Filed: March 1, 1971 Appl. No.: 119,783

[7 3] Starnberg,

[30] Foreign Application Priority Data March 26, 1970 Germany ..P 20 14 870.3 Aug. 25, 1970 Germany ..P 20 41 985.6

References Cited UNITED STATES PATENTS 8/1914 Fuchs ..175/394 X 10/1951 McClinton 175/394 [451 Nov. 21, 1972 3,605,921 9/1971 Mayer ..175/394 FOREIGN PATENTS OR APPLICATIONS 22,192 4/1921 France ..l75/394 Primary Examiner-Marvin A. Champion Assistant Examiner-Richard E. Favreau Attorney-W. G. Fasse [5 7 ABSTRACT The present rock drilling bit comprises along its shaft portions of asymmetrical cross sectional areas for strengthening the drilling bit. These asymmetrical portions are distributed along and around the central axis of the shaft in such a manner that a curve which interconnects the surface centers of gravity of these portions which are located off said central axis, forms a spiral helix. These portions may be located in preferred sections of the drill bit shaft, especially in a transitionary section between the tip of the drill bit and the shaft proper or in another transitionary section between the shaft and a shank of the drilling bit.

11 Claims, 8 Drawing Figures SHANK 0R TIP l4 O TlP OR SHANK PKTENTED Nov 2 1 1912 sum 1 or 2 INYENTORS. OTTO BOHM BY WERNER SCHOLZ G.G.M I

ATTORNEY.

PATENTEDnum 1912 3.703214 SHEET 2 [IF 2 SHANK OR TIP FIG. 7 FIG. 8

my R3.

OTTO BO BY WERNER SCHOLZ ATTORNEY ROCK DRILLING BIT BACKGROUND OF THE INVENTION The present invention relates to a rock drilling bit, especially one for use in connection with a torsional impact drilling machine. More particularly, the invention relates to drilling bits comprising a shaft with one or two feed screws for removing the borings.

Experience has shown that external forces cause in rock drilling bits special, large loads in sections which form a transition between the tip of the drilling bit and the shaft of the bit. These large loads in said transitionary sections are due to the fact that the bit is relatively freely guided at its shank end which is held in the chuck of the drilling machine, whereas its other end, that is, the end with the tip of the drill bit is rigidly held in the rock formation. This situation corresponds, as far as the bending moments applied to the drilling bit are concerned, to a rod one end of which is rigidly secured to a supporting structure while its other end is subject to a load. In this situation the endangered cross section of the rod is located adjacent or near its secured end. Applied to a rock drilling or drill bit this means that the most endangered section of the bit is located immediately behind the tip of the drill bit. Accordingly, any irregular laterally directed yielding movement of the drill bit is effective in an amplified manner in the transitional area or section between the tip of the drill bit and the shaft.

Conventionally it has been suggested to alleviate the above difficulty in a rock drill bit comprising a double feed screw around its shaft, by strengthening the core of the shaft in said transitionary section in which the large loads occur. The conventional rock drill bit is produced by means of tools which are brought to bear upon a bit blank from two opposite sides. Stated differently, the tools are arranged or displaced about the circumference of the bit blank by 180 degrees. The resulting drill bit has a cross section which in said transitional area or section increases from the bit shaft toward the tip of the bit with each winding of the feed screw, whereby the cross sectional areas of the resulting increasing diameters are respectively symmetrical relative to the longitudinal axis of the drill bit. Stated differently, all of the increasing diameter portions of the drill bit in said transitional area form a symmetric configuration relative to the longitudinal axis of the drill bit.

It has been found that such symmetrical strengthening is still unsatisfactory especially in connection with rock drilling bits to be operated by so called torsional impacting drilling machines.

OBJECTS OF THE INVENTION In view of the foregoing it is the aim of the invention to achieve the following objects, singly or in combination:

to overcome the above outlined drawbacks of the prior art;

to construct a rock drill bit which has an increased rigidity or strength in its transitional sections or areas, especially between the shaft proper and the tip of the drill bit and/or between the shaft and a shank by means of which the drill bit is held in the chuck of the drilling machine;

to provide strengthening means which are suitable for drill bits having either a double feed screw or worm or a single feed screw for the borings;

to increase the effective length of the drill bit shaft, as a manner of speaking, by shaping the shaft so that its effective axis is a helical spiral rather than a straight line, whereby a more favorable force distribution is accomplished; and

to provide a drill bit which may be produced from the same blanks as heretofore by employing the same tools as well as the same tool feed and the same revolutions per minute and so forth, whereby the feed screw or feed screws or the drill bit will have the same geometric configuration along that portion of the shaft length along which the drill bit has constant dimensions while simultaneously providing a larger rigidity or strength in the above mentioned transitional area or areas as compared to prior art drill bits.

SUMMARY OF THE INVENTION According to the invention there is provided a rock drilling bit in which the shaft or at least certain transitionary sections of the shaft have portions of increased dimensions relative to a central longitudinal axis of the shaft, whereby these portions are distributed around the shaft in such a manner that the surface centers of gravity of all cross sectional areas are located on a curve having substantially the shape of a spiral helix extending around the longitudinal central axis of the drill bit. This teaching is applicable to drill bits having a double feed screw as well as to drill bits with a single feed screw for the borings.

Stated differently, this means that the peripheral surface of the drill bit core which simultaneously forms the bottom of the feed screw has the shape of a spiral helix in the area of the strengthening, that is, in the transitionary area. One possibility of producing the present drill bit with two feed screws is to machine the two screw windings by means of cutting tools both of which begin their respective cutting operation from the same generatrix and both of which are fed uniformly inwardly in the radial direction relative to the longitudinal axis of the drill bit shaft.

BRIEF DESCRIPTION OF THE DRAWINGS:

In order that the invention may be clearly understood, it will now be described by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 illustrates a partial side view of a rock drilling bit according to the invention comprising two feed screws in the transitionary area showing the strengthened portion but omitting the remaining portions of the drill bit in order to save space;

FIG. 2 is an axial central section through the portion shown in FIG. 1;

FIG. 3 is a cross sectional view through the rock drill bit along line 3-3 of FIG. 1;

FIG. 4 is a cross sectional view through the the rock drill bit according to FIG. 1 but along line 44;

FIG. 5 illustrates a sectional view along line 5-5 in FIG. 1;

FIG. 6 is a view similar to that of FIG. 1 but showing a rock drill bit having a single feed screw and also illustrating the transitional area where the shaft of the drill bit is strengthened;

FIG. 7 is a sectional view along lines 7-7 in FIG. 6; and

FIG. 8 is a sectional view along lines 88 in FIG. 6.

DESCRIPTION OF EXAMPLE EMBODIMENTS:

In FIG. 1 the partial view of the drill bit 11 shows a portion of the shaft 1 the bit tip or shank of which is symbolized by the arrow 12 and the shank or tip of which is indicated by the arrow 13. Stated differently, it is irrelevant whether the dimensions to be described below increase from the shank to the tip or vice-versa. The shank 13 is in practice adapted to be held in a chuck of a drilling machine not shown. The shaft 1 of the drill bit is provided with two feed worms or threads a and b. According to the invention, the dimensions and geometric shape of two adjacent screw windings are the same relative to each other. Thus, the thread winding al of one screw has the same dimension and configuration as the thread winding b1 of the other screw. The same applies with regard to the thread windings a2 and b2.

The core 2 is provided with portions of enlarged diameter which are located in the transitionary area between the tip 12 and the core portion of uniform diameter. The portions which have the largest cross sectional dimensions relative to the longitudinal axis 14 of the drill bit 11 are located immediately adjacent to the tip 12 of the drill bit as indicated by the thick windings a1 and bl. The dimension of the core portions then gradually decreases in the direction toward the shank 13 as indicated by the windings a2 and b2. Further down toward the shank 13 the constant dimension of the core of the shaft is illustrated by the windings a and b. This is particularly illustrated in the sectional view of FIG. 3 where the core 2 has a circular cross section along its length of constant diameter.

The teaching of the invention that adjacent portions of the shaft but belonging to two different screws shall have the same lateral dimension is clearly illustrated in FIG. 2, wherein it is seen that the radii of two adjacent portions are the same relative to the same generatrix 15 or 16 or 17 or 18, whereby said adjacent core portions are arranged one on top of the other. It will be noted that the radial dimensions decrease in steps from the tip in the direction toward the shank 13. Thus, in the example embodiment of FIG. 2 the largest diameter R1 is shown adjacent to the tip 12, whereas the next smaller diameter R2 is located intermediate the constant diameter R3 which is also shown in the sectional view of FIG. 3. The stepwise decrease of the radial dimensions as shown in FIG. 2 results from the fact that the cutting tools are advanced radially during the formation of the screw windings by radial distances corresponding to R1 minus R2 or R2 minus R3 respectively during one full revolution or turn of the shaft blank.

As mentioned, FIG. 3 illustrates the cross sectional area through a portion of the shaft having a constant diameter, whereby the core 2 of the shaft has a constant circular cross section as indicated by the radius R3.

The section illustrated in FIG. 2 is located in an area wherein the shaft is provided with portions of increased dimensions. Such portion 19 bulges, for example, to the left of the center axis 14 of FIG. 4, whereby an asymmetric configuration of the cross sectional area results. Thus, the core 2 and the laterally bulging portion 19 have together a cross sectional configuration or shape corresponding approximately to that of an egg, whereby the center of gravity SP of this egg shape is located off center relative to the central axis 14.

The foregoing considerations also apply to the sectional view of FIG. 5 except that now the larger bulging portion 20 extends laterally to the right of the central axis 14 and accordingly the center of gravity SP1 is located to the right of the central axis 14. The core 2 of the shaft and the enlarged portion 20 form again a sectional configuration having the approximate shape of an egg 4. The curve which interconnects the centers of gravity SP and SP1 and any additional such centers of further cross sectional surfaces, forms a spiral helix which winds itself around the central axis 14.

The drill bit 21 of FIG. 6 comprises a single screw or worm 22 extending around a core 23 in the form of a helix The diameter of the core is indicated at R6 and such diameter increases continuously, that is, without steps through the diameter R5 toward the diameter R4 where the core proper is provided with portions of increased radial dimensions as taught by the present invention. Neither the tip of the drill bit nor its shank are shown because the area comprising the portions of increased radial dimensions may be located in a transitional section between the tip and the shaft or between the shaft and the shank depending on the particular purpose for which the drill bit is intended. Here again the dimensions may increase from the tip to the shank or from the shank to the tip.

FIGS. 7 and 8 illustrate sectional views along respec- I tive lines in FIG. 6. It can be clearly seen in these figures that the cross section of the core 23 is asymmetrical in each place where there is a portion of increased radial dimension. Thus, the portion 24 in FIG. 7 bulges to the left and has a center of gravity SP2 which is off center relative to the central axis 25. The same applies to FIG. 8 however, here the portion 26 having the increased radial dimension bulges to the right of the central axis 25 so that the center of gravity SP3 is also located to the right and off the central axis 25.

Here again, a curve interconnecting the mentioned centers of gravity will form a spiral helix extending around the central axis 25. The cross sectional configurations of the portions 25 and 26 also have the approximate outline of an egg.

The increased rigidity or strength of the present drill bit as compared to prior art rock drill bits may be explained substantially as follows, whereby comparable data or parameters are assumed as a basis for comparison. First, the continuous surface which is controlling for the rigidity of the cross section of the drill bit shaftis larger than the comparable surface of the known drill bit because the cross sectional area in known drill bits is symmetrical relative to the longitudinal central axis so that merely the cross sectional area corresponding to the area of a respective circle can be taken into consideration for calculating the rigidity of the respective cross section. Contrary thereto, according to the invention, the surface center of gravity which is a determining factor in ascertaining the rigidity of any given cross sectional area is displaced relative to the central axis of the drill bit. The displacement of said surface centers of gravity resultsin an increased torsional rigidity because the outer torsional moment for a given cross section is equal to the sum of all static moments resulting from all outer or external forces relative to the tangent to the connecting line or curve of all surface centers of gravity in the respective center of gravity of the particular cross section. Accordingly, the point or rather line in which the torsional force is effective is not the central longitudinal axis of the drill bit but the connecting curve of all surface centers of gravity which curve has the shape of an approximate spiral helix extending around the longitudinal central axis of the drill bit.

Restating the foregoing in more figurative terms, it means that, relative to the bending and torsional moments which are applied to any particular cross section, such moments are not concentrated on the shorter longitudinal central axis of the drill bit in those areas where the portions of increased dimensions are located as is the case in the conventional symmetrically shaped drill bit, but these moments are rather effective along the longer curve which interconnects said centers of gravity of the cross sectional surfaces in the manner of a spiral helix. This means that a more advantageous distribution of the forces and thus of the tensile forces which are effective in any particular cross section in the areas where the portions such as 19 and 20 or 24 and 26 are located. Thus, a drill bit according to the invention which otherwise has the same geometrical conditions or features as a conventional drill bit, especially the same outer diameter, is more resistant or rather stronger than a conventional rock drill bit, against torsion and against bending as well as against a combination or superimposition of these load conditions. I

When producing the present rock drilling bits, for example, by means of milling or whirling care must be taken that the beginning of the cutting operation of several cutting tools, the number of which corresponds to the number of the desired feed screws, starts at an are advanced simultaneously in the radial direction for producing said portions of increased radial dimensions.

According to the invention the present teaching is applicable to drill bits having one or more feed screws for the borings. In connection with the application of the present teachings to drill bits having but one feed screw, the invention is based on the recognition that the stress considerations or problems which occur in the transitionary area between the shaft and the tip of drill bits having two feed screws, are also applicable in a quite similar manner in connection with drill bits having a shaft which is formed to comprise a single feed screw. The practice has shown that generally the cross sections that are most likely to tear are those located in transitionary sections or areas between the shaft of the drill bit and the tip or between the shaft and the shank. Although this experience applies equally to drill bits with one feed screw as well as to drill bits with two feed screws, those skilled in the art applied the idea of strengthening the core or shaft of the drill bit in the endangered transitionary areas only in connection with rock drilling bits having two feed screws because in these shafts, as distinguished from the shaft having but one feed screw, substantially more material must be removed, for example, by turning, whereby it is assumed that in both instances a blank having the same outer diameter is used. However, this consideration does not take into account the fact that especially in the endangered transitionary areas of the shaft of the drill bit, screw windings are present which have the same dimensions in the double feed screw shaft as well as in the single feed screw shaft. Accordingly, these transitionary areas constitute to the same extent in both instances weak spots for the mechanical strength of the drill bit shaft.

It is the merit of this invention to have recognized the just outlined considerations and thus to apply the present teaching of strengthening the transitionary zone either between the tip and the shaft proper or between the shaft and the shank. It is also possible to provide these strengthening portions in both transitionary areas, namely between the shank and the shaft as well as between the shaft and the tip.

Although specific embodiments have been described, it is to be understood that the present invention is intended to cover all modifications and equivalents within the scope of the appended claims.

What we claim is:

1. In a rock drilling bit having a shaft with a longitudinal central axis therethrough, a bit tip at one end of said shaft, a shank at the opposite end of said shaft, and worm means extending around said shaft from said bit tip to said shank for removing borings, the improvement comprising shaft portions of different dimensions measured perpendicularly relative to said central axis, whereby said shaft portions have cross sectional areas of asymmetric shape relative to said central axis, each of said cross sectional areas having a surface center of gravity, said portions being distributed along said shaft and having such dimensions that a curve interconnecting said surface centers of gravity constitutes substantially a spiral helix extending around said central axis.

2. The rock drilling bit according to claim 1, wherein said worm means comprise a single screw.

3. The rock drilling bit according to claim 1, wherein the dimensions of said portions increase toward said bit tip and decrease toward said shank.

4. The rock drilling bit according to claim 1, wherein the dimensions of said portions decrease toward said bit tip and increase toward said shank.

5. The rock drilling bit according to claim 1, wherein said shaft has a central core of circular cross section and located so that its axis coincides with said central axis.

6. The rock drilling bit according to claim 1, comprising a central core, a section of uniform core diameter adjacent to said shank, and a transitionary section between said bit tip and said uniform diameter section, said shaft portions of different dimensions being located in said transitionary section in such a manner that the cross sectional area increases toward said bit tip and decreases from said bit tip toward said uniform diameter section.

7. The rock drilling bit according to claim 1, comprising a central core section of uniform core diameter adjacent to said bit tip, and a transitionary section between said shank and said uniform diameter section,

said shaft portions of different dimensions being located in said transitionary section in such a manner that the cross sectional area increases toward said shank and decreases from said shank toward said uniform diameter section.

8. The rock drilling bit according to claim 1, wherein said worm means comprise two separate screws.

9. The rock drilling bit according to claim 8, wherein each of said two screws has its own portions of different dimensions such that the radial dimension of a portion of one of said screws is equal to the radial dimension of an adjacent respective portion of the other screw relative to the same generatrix.

10. A rock drilling bit comprising a shaft having a longitudinal central axis, a bit tip at one end of the shaft, a shank at the opposite end of the shaft, first and second worms extending around said shaft between said bit tip and said shank for removing borings, a transitional section forming part of the shaft adjacent to said bit tip, and shaft portions of different cross sectional dimensions located in said transitional area so that the cross sectional areas of the shaft increase toward said bit tip and decrease toward said shank, said different cross sectional dimensions having an asymmetrical shape relative to said central axis and surface centers of gravity so that a curve connecting said surface centers of gravity constitutes substantially a spiral helix extending around said central axis.

11. A rock drilling bit comprising a shaft having a longitudinal central axis, a bit tip at one end of the shaft, a shank at the opposite end of the shaft, a single worm extending around said shaft between said bit tip and said shank for removing borings, a transitional section forming part of the shaft adjacent to said shank, and shaft portions of difierent cross sectional dimensions located in said transitional area so that the cross sectional areas of the shaft increase toward said shank and decrease toward said bit tip, said different cross sectional dimensions having an asymmetrical shape relative to said central axis and surface centers of gravity so that a curve connecting said surface centers of gravity constitutes substantially a spiral helix extending around said central axis.

Ill i 3 

1. In a rock drilling bit having a shaft with a longitudinal central axis therethrough, a bit tip at one end of said shaft, a shank at the opposite end of said shaft, and worm means extending around said shaft from said bit tip to said shank for removing borings, the improvement comprising shaft portions of different dimensions measured perpendicularly relative to said central axis, whereby said shaft portions have cross sectional areas of asymmetric shape relative to said central axis, each of said cross sectional areas having a surface center of gravity, said portions being distributed along said shaft and having Such dimensions that a curve interconnecting said surface centers of gravity constitutes substantially a spiral helix extending around said central axis.
 1. In a rock drilling bit having a shaft with a longitudinal central axis therethrough, a bit tip at one end of said shaft, a shank at the opposite end of said shaft, and worm means extending around said shaft from said bit tip to said shank for removing borings, the improvement comprising shaft portions of different dimensions measured perpendicularly relative to said central axis, whereby said shaft portions have cross sectional areas of asymmetric shape relative to said central axis, each of said cross sectional areas having a surface center of gravity, said portions being distributed along said shaft and having Such dimensions that a curve interconnecting said surface centers of gravity constitutes substantially a spiral helix extending around said central axis.
 2. The rock drilling bit according to claim 1, wherein said worm means comprise a single screw.
 3. The rock drilling bit according to claim 1, wherein the dimensions of said portions increase toward said bit tip and decrease toward said shank.
 4. The rock drilling bit according to claim 1, wherein the dimensions of said portions decrease toward said bit tip and increase toward said shank.
 5. The rock drilling bit according to claim 1, wherein said shaft has a central core of circular cross section and located so that its axis coincides with said central axis.
 6. The rock drilling bit according to claim 1, comprising a central core, a section of uniform core diameter adjacent to said shank, and a transitionary section between said bit tip and said uniform diameter section, said shaft portions of different dimensions being located in said transitionary section in such a manner that the cross sectional area increases toward said bit tip and decreases from said bit tip toward said uniform diameter section.
 7. The rock drilling bit according to claim 1, comprising a central core section of uniform core diameter adjacent to said bit tip, and a transitionary section between said shank and said uniform diameter section, said shaft portions of different dimensions being located in said transitionary section in such a manner that the cross sectional area increases toward said shank and decreases from said shank toward said uniform diameter section.
 8. The rock drilling bit according to claim 1, wherein said worm means comprise two separate screws.
 9. The rock drilling bit according to claim 8, wherein each of said two screws has its own portions of different dimensions such that the radial dimension of a portion of one of said screws is equal to the radial dimension of an adjacent respective portion of the other screw relative to the same generatrix.
 10. A rock drilling bit comprising a shaft having a longitudinal central axis, a bit tip at one end of the shaft, a shank at the opposite end of the shaft, first and second worms extending around said shaft between said bit tip and said shank for removing borings, a transitional section forming part of the shaft adjacent to said bit tip, and shaft portions of different cross sectional dimensions located in said transitional area so that the cross sectional areas of the shaft increase toward said bit tip and decrease toward said shank, said different cross sectional dimensions having an asymmetrical shape relative to said central axis and surface centers of gravity so that a curve connecting said surface centers of gravity constitutes substantially a spiral helix extending around said central axis. 